Power control for an asynchronous multirate decorrelator

For code-division multiple-access (CDMA) wireless systems employing multius er detection, the varied bit-error rate (BER) requirements of multimedia tr affic dictate the use of transmitted power control, Using a decorrelator in an asynchronous multirate direct-sequence CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation lo sses to varying degrees depending on individual requirements. In this conte xt, we propose a power control algorithm for a multirate decorrelator that is suitable for a class of BER-based link quality objectives. If the uplink channel gain of the desired user is known, then it is straightforward for each user to choose the transmitted power needed to meet its target BER obj ective. In practice, however, the uplink channel gain is often difficult to measure, Tn avoid this measurement, we employ stochastic approximation met hods to develop a simple iterative power control algorithm. In this algorit hm, each mobile uses the output of its own decorrelator to update its trans mitted power in order to achieve its BER objective. We show that when a use r's bits have nonzero asymptotic efficiencies, the power control algorithm converges quickly in the mean square sense to the minimum power at which a user achieves its quality of-service objective.